1. FIELD OF THE INVENTION
The present invention relates to an apparatus for monitoring a predetermined treatment effected on objects successively moved along a given path, and particularly relates to an apparatus for monitoring whether a predetermined treatment has been effected, at a predetermined working station, on each of objects which are successively moved to the working station along a predetermined path.
2. DESCRIPTION OF THE RELATED ART
In a system in which a predetermined treatment, such as printing of desired characters, marks, etc., laser machining or the like, is effected on objects successively transported by transporting means such as a conveyer line, generally, monitoring is made as to whether the predetermined treatment has been effected on the objects or not.
For example, there is a system in which desired items such as a product number, a production date, and so on are printed by an ink jet printer on objects successively transported by means of a conveyer line. Such a system is provided with a printer having a print head disposed opposing the conveyer line, an object sensor for producing a detection signal when the sensor detects that a leading end of each object has reached a position opposing the print head, and print control means including a microcomputer for controlling the printer so that the printer executes a predetermined printing operation in response to the detection signal.
The microcomputer of the print control means has a timer function to start counting of clock pulses in response to the detection signal of the sensor so as to produce a signal when the count value has reached a value corresponding to a predetermined time interval. Further, the microcomputer executes data processing including preparation of data to be used for controlling the print head in order to print the above-mentioned items on each of the objects in response to an output signal of the timer function, for example, data of binary codes of characters when the item is the characters, and storing the prepared data in a predetermined register. Upon completion of the data processing, the microcomputer produces a printing start signal.
Theoretically, the above-mentioned predetermined time interval must be equal to the time interval required for each of the objects to move a distance from the leading end of the object to a starting point of the printing on the object subtracted by a time interval usually required for the microcomputer to execute the data-processing. However, since the latter is negligibly small as compared with the former in normal case, there is no significant problem in practical application by setting the predetermined time interval at a value equal to the former. Accordingly, upon generation of the printing start signal, the printing start position on the object is opposing to the print head. The print control means includes means for causing the printer to start its printing operation in response to the printing start signal so that the printer prints the above-mentioned items on the object by using data stored in the register.
In the conventional printing system, however, there is a problem that the timer function of the microcomputer operates erroneously or the microcomputer fails to execute the above-mentioned data processing because the data processing may be complicated depending on the contents of the item, so that the printing start signal is not generated and printing is not started though the printing start position of the object has reached the position opposing the print head to thereby allow the object to be conveyed without being printed.
For example, as disclosed in Japanese Utility Model Publication No. JP-A-61-138054 (UM), it is known to provide a microcomputer with a watch dog timer function to detect erroneous operation of the microcomputer to thereby monitor whether the microcomputer is executing a predetermined calculation processing operation. By use of such a watch dog timer function, it is possible to detect erroneous operation of the timer function of the microcomputer. However, the watch dog timer function judges that the microcomputer is normal so long as the timer function operates normally, and it is therefore impossible to detect an event such that the microcomputer fails to execute the data processing because it is complicated. Accordingly, by means of the above-mentioned known technique, it is impossible to reliably detect the object transported without being printed.